1. Field of the Invention
The present invention relates to measurement of alternating current line voltage and more particularly to a system for measuring variations in line voltage and taking such variations into account to make appropriate changes in the operation of an associated system such as an air conditioner or a microwave oven, etc.
2. Background Art
A search of the background art directed to the subject matter of the present invention conducted in the U.S. Patent and Trademark Office disclosed the following U.S. Letters Patent.
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Based on a thorough review of the above identified patents, we believe that none of the above teach, disclose or claim the novel combination of elements and functions found in the improved system taught by the present invention.
In many systems, notably microwave ovens, air conditioning systems, etc., microprocessors are employed to monitor alternating current line voltage. In microwave ovens, as the line voltage varies, the output power varies and consequently this can affect or change the cooking characteristics. If the line voltage is known, such variations can be taken into account and appropriate changes can be made in cooking time for consistent cooking. In an air conditioner, as line voltage drops, current in the compressor will rise and cause over heating. With proper monitoring of the line voltage, the compressor may be shut off before over heating occurs.
A great many techniques have been developed for monitoring line voltage. Many techniques employed for line voltage measurement utilize a comparator. One of the inputs to the comparator would be a reference point set up by a regulated supply. The reference point would then represent a certain voltage level. The second input would be that of the AC line conditioned to provide a stable comparison voltage. Should this voltage drop below the reference point, the comparator would operate indicating that the reference voltage has been reached. Voltage then would have to rise to a certain level for the comparator to return to its original state. Where great accuracy is needed, the method will not function because the circuitry requires a very accurate reference point. Should great accuracy not be required, the values may be approximated. But errors can occur because of the tolerance of the regulated supply, the accuracy of resistor dividers employed as a reference point and the circuitry to condition the AC voltage. Any such errors will cause the desired numbers to vary frequently from the approximated value. The control then would have to be calibrated to give an accurate reference point. Such calibration of controls is done manually, usually with some type of potentiometer to vary the reference point. Any variations due to the load of the transformer are taken into account by coming up with a fixed offset through testing. The same offset would be used by all controls for a given application. This sort of circuit frequently employs a lot of parts and only allows the monitoring of one or two different points on the line, thus calibration is time consuming and still presents the possibility of inaccuracy.
Other techniques include the utilization of a memory to store a look up table for stored values being equivalent to power supply inputs which are then provided by control of the output. In such an arrangement, where the output changes new value is used to control the input causing performance characteristics to remain stable.
Another technique involves the storing of a particular desired factor in the program's memory with adjustments of output voltage based on a particular desired temperature or operating level to be employed.
Other techniques include the measuring of the width of pulses to determine proper operation. As the input alternating current voltage changes, the width of the pulse changes and accordingly steps are taken to make the appropriate corrections in the output voltage.
Accordingly, it is object of the present invention to provide a new and useful alternating current voltage monitoring technique with an associated appropriate control which overcomes the shortcomings of the prior art.